The present invention relates to compound semiconductor devices, e.g., a light emitting diode or a semiconductor laser, and methods of making compound semiconductor devices.
II-VI compound semiconductor devices are expected to be light emitting devices which can emit short wavelength light, e.g., green or blue.
Electronics Letters, vol.29, No.16, pp. 1488-1489 (1993) discloses a semiconductor laser composed of a II-VI compound semiconductor. An n-clad layer of n-ZnMgSeS, an n-waveguide layer of n-ZnSe, a multi-quantum well (MQW) layer of CdZnSe, a p-waveguide layer of p-ZnSe, a p-clad layer of p-ZnMgSe, a p-contact layer of p-ZnSeS and a mesa-shaped p-contact layer of p-ZnSe are formed on a substrate of n-GaAs, sequentially.
An insulator layer is formed on the p-contact layer of p-ZnSeS so that the insulator layer and the mesa-shaped p-contact layer cover the p-contact layer of p-ZnSeS. Thus, the laser includes an external current blocking structure between the semiconductor device and the external electrode. A p-side electrode of Pd/Pt/Au is formed on the p-contact layer of p-ZnSe, and an n-side electrode of In is formed on the substrate.
In II-VI compound semiconductor devices, it has been difficult to obtain good ohmic contact. Therefore, the laser in he above-mentioned article requires a high voltage to emit light, e.g., more than 10 V, which is higher relative to the energy of emitted light, e.g., about 2.5 V.
Further, the external current blocking structure causes poor heat radiation efficiency and poor current injection efficiency, since the area where the p-side electrode contacts with the mesa-shaped p-contact layer is small. However, it is difficult to obtain an internal current blocking structure.
As a result, a temperature of the laser is up during operation and the reliability is deteriorated. Therefore, continuous operation and high reliability have not been obtained in II-VI compound semiconductor devices, yet.
Concerning III-V compound semiconductor devices containing nitrogen (N), Appl. Phys. Lett., vol.48 (1986) pp. 207-208 discloses a semiconductor laser having an internal current blocking structure. However, nitrogen containing ("N-containing") III-V compound semiconductor devices have the same problems as II-VI compound semiconductor devices. Jap. Appl. Phys., vol. 32 (1993) pp.L8-L11 discloses N-containing III-V compound semiconductor devices, i.e., pn junction type light emission diode having a double hetero junction and no current blocking structure. The effective current blocking structure for GaN devices has not been obtained. Therefore, current injection type lasers of GaN, i.e., N-containing III-V compound semiconductor devices, are difficult to produce.